1. Field of Invention
The present invention relates to a color adjustment, and more particularly, to an apparatus for adjusting specific color attributes in an image for different color regions in the color space and a method thereof.
2. Description of Related Art
In the past, many color spaces have been defined to describe various colors. For example, the RGB color space is a Cartesian coordinate system, and red (R), green (G) and blue (B) are respectively three bases of the coordinate system. That is, in the RGB color space, any color can be described with the combination of the three color attributes of red (R), green (G) and blue (B). Although the RGB color space is mostly used in the input and output of image devices like scanners, displays, etc., as there is high relevance between each color attribute of the RGB color space, it is not suitable for image processing such as color adjustment.
Comparatively, the HSI color space is more suitable for the image processing such as color adjustment. The HSI color space is closer to human vision sense and its color attributes have no relevance between each other. Referring to FIG. 1, the HSI color space is a coordinate system having three bases of hue (H), saturation (S) and intensity (I). Hue refers to the kind of color, that is, the color of light with different wavelength sensed by human eyes, such as red, orange, yellow, green and blue. Saturation refers to the purity of color, that is, the degree of white color infiltrating into the color. The higher saturation of color represents the less white infiltrating into the color. Intensity refers to the luminance of color, that is, the closer it is to white, the higher the intensity is, and the closer it is to black, the lower the intensity is. The value of hue is 0°˜360°, and the values of saturation and intensity are 0˜255 if they are represented by 8 bits.
Conventionally, the adjustment for the color of an image is achieved by transforming color attributes through a transformation matrix. However, the color adjusting method using the transformation matrix influences and adjusts each color region in the color space of image. That is to say, it is impossible to perform color adjustment for a certain color range only by rotating the color space through the transformation matrix. Also, although it is more suitable for adjusting color of image in the HSI color space, conventionally, the adjusting manner is not modified for different color regions of the HSI color space to avoid generating some problems when performing color adjustment at regions with acute change in hue. For example, fine-tuning performed near the center of the HSI color space leads to huge changes in saturation or intensity.